Lipid Reserve Dynamics and Magnification of Persistent Organic Pollutants in Spawning Sockeye Salmon (Oncorhynchus nerka) from the Fraser River, British Columbia

Abstract

Pacific sockeye salmon (Oncorhynchus nerka) can travel several hundred kilometers to reach native spawning grounds and fulfill semelparous reproduction. The dramatic changes in lipid reserves during upstream migration can greatly affect internal toxicokinetics of persistent organic pollutants (POPs) such as PCBs, PCDDs, and PCDFs. We measured lipid content changes and contaminant concentrations in tissues (liver, muscle, roe/gonads) and biomarker responses (ethoxyresorufin O-deethylase or EROD activity and CYP1A levels) in two Pacific sockeye salmon stocks sampled at several locations along their spawning migration in the Fraser River, British Columbia. Muscle lipid contents declined significantly with increasing upstream migration distance and corresponded to elevated lipid normalized concentrations of PCBs and PCDD/Fs in spawning sockeye. Post-migration magnification factors (MFs) in spawning sockeye ranged between 3 and 12 and were comparable to model-predicted MFs. sigmaPCBs(150-500 ng x g(-1) lipid), sigmaPCDD/Fs (1-1000 pg x g(-1) lipid) and 2,3,7,8-TCDD toxic equivalent or TEQ levels (0.1-15 pg x g(-1) lipid) in spawning sockeye were relatively low and did not affect hepatic EROD activity/CYP1A induction. Despite a 3-fold magnification, TEQ levels in eggs of spawning Fraser River sockeye did not exceed 0.3 pg x g(-1) wet wt, a threshold level associated with 30% egg mortality in salmonids. PCBs in Fraser River sockeye are comparable to previous levels in Pacific sockeye. In contrast to Pacific sockeye from more remote coastal locations, PCDDs and PCDFs in Fraser River sockeye were generally minor components (<25%) of TEQ levels, compared to dioxin like PCB contributions (>75%). The data suggest that (i) the Fraser River is not a major contamination source of PCBs or PCDD/Fs and (ii) marine contaminant distribution, food-chain dynamics, and ocean-migration pathway are likely important factors controlling levels and patterns of POPs in returning Pacific sockeye. We estimate an annual chemical flux entering the Fraser River of up to 150 g for sigmaPCBs and 40 mg for sigmaPCDD/ Fs via returning sockeye. The results indicate that historical concentrations of PCBs and PCDD/Fs remain a potential threat to organism and ecosystem health on the west coast of Canada.

Tissue residue concentrations of organohalogens and trace elements in adult Pacific salmon returning to the Fraser River, British Columbia, Canada

“…We observed relatively high MFs (8-12) of lipophilic OCPs (e.g., DDTs, chlordanes, octachlorostyrene, and mirex), but only in muscle of Adams River sockeye. The observed MFs in Fraser River sockeye and chinook are consistent with previously reported postmigration MFs of PCB and PCDD/F congeners in spawning Pacific salmon [18,19,29]. Conversely, tetra-and pentachlorobenzenes and HCH isomers exhibited relatively low MFs (range 0.1-1.7), likely attributable to efficient elimination of these compounds via gill ventilation and lipid-to-water exchange processes [30,31].…”

“…The observed magnification of recalcitrant lipophilic compounds is attributable to the combination of rapid lipid reserve depletion and slow chemical elimination kinetics in these salmon during this period [18,19]. Conversely, lipid-corrected concentrations of HCHs were in some cases significantly lower ( p < 0.05) in fish sampled near spawning grounds compared with concentrations in fish sampled in the lower Fraser River (Fig.…”

“…during upstream migration [18,19]. Returning Pacific salmon generally stop feeding after entering freshwater.…”

“…Observed postmigration magnification factors (MFs) of PCBs and PCDD/Fs in various tissues of Pacific salmon, determined as the ratio of lipid-normalized concentrations observed at post-and premigration locations, ranged between approximately 1 and 12 [18,19]. Debruyn et al [18] developed a model to predict migration-related magnification and chemical redistribution from pre-and postmigration tissue weights (W i ) and corresponding pre-and postmigration lipid fractions (L i ).…”

Utilisation des poissons pour évaluer les effets biologiques des contaminants dans l’estuaire du Saint-Laurent et le fjord du Saguenay

“…Sur le terrain, les effets biologiques et les concentrations de PBT dans les tissus cibles doivent être déterminés au moment où les risques d'impacts sont les plus grands, soit à la fin de la période de jeûne ou de migration. Des modèles numériques devraient être développés pour prédire les changements de concentrations des PBT dans des tissus cibles sous différents scénarios de conditions environnementales et pour prédire les impacts de ces changements sur la croissance, la survie ou la reproduction (KELLY et al, 2007). (SCOTT et SCOTT, 1988).…”